curl --request POST \
  --url https://api.getsly.ai/v1/v1/settlement-windows/holidays \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "date": "<string>",
  "rail": "<string>",
  "name": "<string>"
}
'

{
  "data": {
    "date": "<string>",
    "rail": "<string>",
    "name": "<string>",
    "source": "system"
  }
}